Biomedical subjects

C R Breese

Publications and source records attributed to C R Breese.

21 records · Page 2Linked to original sources

PubMed1991

Distribution of insulin-like growth factor 1 (IGF-1) and 2 (IGF-2) receptors in the hippocampal formation of rats and mice.

This study demonstrated species differences in IGF-1 and IGF-2 receptor binding and localization in the hippocampus of the rat and mouse. Competition binding studies indicated that there were no differences in the relative binding affinities for the type 1 or type 2 receptors between the brains of these animals. These results suggested that the observed species differences were not attributable to alterations in IGF receptor kinetics. Receptor autoradiographic analyses demonstrated that IGF-1 binding differed in both the localization and overall receptor densities observed, with the rat demonstrating more specific localization and greater receptor density in the hippocampus than the mouse. The rat also exhibited a greater density of IGF-2 receptors in the hippocampus than the mouse. Despite differences in IGF receptor populations, both species exhibit similar hippocampal structure and lamination. Therefore, these results demonstrate a disparity in the localization of IGF receptor binding in the rat and mouse, suggesting that IGFs in these species are differentially regulated, with distinct neuromodulatory, neurotrophic, and/or developmental roles in this region of the brain. Previous comparative anatomical studies of the hippocampal formation of rats and mice fail to offer an explanation for the absence or reduction of binding of IGF-1 in the mouse. Although the mouse has a greater cell density in the s. granulosum than the rat, and both species exhibit similar glia and synaptic contact densities in the s. moleculare of the dentate gyrus, the mouse exhibits a complete absence of IGF-1 binding in this region. The lack of anatomical differences in the hippocampal formation of these species suggests that the patterns observed in IGF binding result from alterations in either neurochemical modulation of these neurons or specific neurotrophic requirements of the cells in this region. Differences have been reported on the concentrations and binding of various neurotransmitters in the hippocampus of these species, however these differences do not easily account for the variations observed in IGF binding in this study. IGFs are known to influence acetylcholine neurotransmission in the hippocampus as well as other brain areas in the rat. Recently, a truncated form of IGF-1, in which a tripeptide is cleaved from the N-terminus of the peptide, has been reported in brain. The cleaved tripeptide has been shown to activate glutamate receptors, which may dramatically influence excitatory neurotransmission in this region. Therefore, in addition to the possible neurotrophic actions of the peptide itself, subsequent processing of IGF-1 may be an important aspect of IGF-1 activity in the brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1991

Influence of age and long-term dietary restriction on plasma insulin-like growth factor-1 (IGF-1), IGF-1 gene expression, and IGF-1 binding proteins.

The purpose of these studies was to determine more accurately the relationship between IGF-1 and life span, and to determine whether moderate dietary caloric restriction alters the age-related changes in IGF-1. Studies included an assessment of plasma IGF-1, hepatic IGF-1 mRNA, and plasma IGF-1 binding proteins (IGF-1-BP). Rats (6, 12, 22, and 28 months of age) were fed ad libitum or maintained on a diet 60% of ad libitum. In ad libitum fed animals, plasma IGF-1 decreased by 20% between 6 and 28 months of age. Similar age-related declines were observed in dietary restricted animals but levels were generally 14-25% lower at each age group. IGF-1 mRNA levels demonstrated similar decreases with age in ad libitum fed animals, but in dietary restricted animals, levels plateaued at 22 and 28 months. IGF-1 binding protein analysis revealed 3 bands at approximate molecular weights of 40k, 30k, and 24k. All bands demonstrated a decrease in relative IGF-1-BP concentration with age, as well as a decrease in the 40k and 30k binding proteins after dietary restriction. These results indicate that (a) aging in ad libitum fed animals is associated with decreases in plasma IGF-1, IGF-1-BP, and IGF-1 mRNA levels; and (b) long-term dietary restriction decreases plasma IGF-1 and IGF-1-BP levels in each age group although the age-associated decreases in IGF-1 mRNA levels are prevented by dietary restriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1989

Hippocampal place cells: stereotypy and plasticity.

Hippocampal complex spike cells were recorded during exploration for water delivered to cups located in various regions of an elevated platform. Place fields were recorded with a video monitoring system that recorded movements as the animal explored each of the 5 cup locations where water was delivered on the platform. Plasticity of place cell firing as a function of selective water delivery to specific cup locations on the platform was also examined. Several characteristics of place cell firing were studied that indicated a high degree of control by factors such as relative direction of movement and trajectory through the field. Time-shift analyses indicated cell firing was most representative of the place field at the time of spike occurrence. It was demonstrated that place fields possess borders in which firing was increased or decreased upon entering or leaving a particular region of the platform. The most important finding from this investigation was the pronounced degree of plasticity exhibited by place cells. Selective delivery of water to a single location on the platform was sufficient in most of the cases tested to shift the location of the field to the location where water was available. These findings suggest hippocampal place cell firing, although highly influenced by spatial and directional features of the environment, can readily change under conditions in which significant stimuli are added or removed from those locations.

Animals↗